In the field of automobiles, in order to implement improvement in environmental friendliness, safety and amenity, development not only of a vehicle controlling system such as an antiskid brake system (Electronic Stability Control: hereinafter referred to as ESC) for preventing spinning, off the track and so forth during turning but also of a vehicle controlling system which uses an intelligent transportation system (Intelligent Transport System: hereinafter referred to as ITS) such as a vehicle distance control (Adaptive Cruise Control: hereinafter referred to as ACC), a lane departure prevention system or pre-crash safety is being accelerated.
The ESC is vehicle motion control based on the concept of Direct Yaw-moment Control (DYC) (refer to Non-Patent Document 1).
This DYC is a technique for controlling the yawing moment for directly promoting or restoring a yawing motion, which is rotation around a Z axis of a vehicle, by providing a difference in braking forces or driving forces between the left and right wheels in order to improve the drivability and stability of the vehicle as described in Non-Patent Document 1.
Also a method is available by which acceleration or deceleration is performed automatically in conjunction with a lateral motion caused by a steering operation to give rise to a load movement between the front wheels and the rear wheels thereby to achieve improvement in drivability and stability of the vehicle (refer to Non-Patent Document 2).
The acceleration/deceleration instruction value for performing acceleration/deceleration automatically (target longitudinal acceleration Gxc) is such as represented by the Formula 1 given below.
                                                        G              xc                        =                                                            -                                      sgn                    ⁡                                          (                                                                        G                          y                                                ·                                                                              G                            .                                                    y                                                                    )                                                                      ⁢                                                      C                    xy                                                        1                    +                    Ts                                                  ⁢                                                                                              G                      .                                        y                                                                                +                              G                                  x                  ⁢                                                                          ⁢                                      _                    ⁢                    DC                                                                                ⁢                                          ⁢                                          ⁢                                                  ⁢                                                          ⁢                              G                .                            ⁢              y                        =                          G                              y                ⁢                                                                  ⁢                _                ⁢                                                                  ⁢                dot                                                    ⁢                                                      [                  Formula          ⁢                                          ⁢          1                ]            
This formula indicates a simple control strategy that basically a value obtained by multiplying the lateral jerk Gy_dot by a gain Cxy to apply a primary delay is used as a forward/rearward or longitudinal acceleration/deceleration instruction.
It is to be noted that Gy: vehicle lateral acceleration, Gy_dot: vehicle lateral jerk, Cxy: gain, T: primary delay time constant, s: Laplace operator, and Gx_DC: offset.
By this, part of a cooperation control strategy of lateral and forward/backward or longitudinal motions of an expert driver can be simulated, and improvement in drivability and stability of the vehicle can be implemented.
Where such control as just described is performed, a composite acceleration (represented by G) of the longitudinal acceleration and the lateral acceleration is vectorized (Vectoring) such that it exhibits a curved transition as time passes on a diagram wherein the axis of abscissa is the longitudinal acceleration of the vehicle and the axis of ordinate is the lateral acceleration of the vehicle. Therefore, the control is called “G-Vectoring control”.
In this G-Vectoring control, the deceleration of the vehicle is controlled in response to the lateral jerk. On the other hand, the ESC controls the yaw moment of the vehicle in response to a lateral slip of the vehicle. Roughly speaking, the G-Vectoring control controls the sum of braking forces by the tires among the four wheels, and the ESC performs control of the difference in braking forces between each two left and right wheels. From such a relationship as just described, in Patent Document 1, a motion controlling apparatus for a vehicle is disclosed which is characterized in that the motion controlling apparatus for a vehicle has a first mode in which substantially equal braking or driving forces are generated by the left and right wheels from among four wheels based on an acceleration/deceleration controlling instruction linked to a lateral motion and a second mode in which different braking or driving forces are generated by the left and right wheels from among the four wheels based on a yaw moment controlling instruction calculated from lateral slip information of the vehicle. When the yaw moment instruction value is low, the motion controlling apparatus for a vehicle operates in the first mode, and when the yaw moment instruction value is high, the motion controlling apparatus for a vehicle operates in the second mode.